This invention relates to a key assembly such as a telephone multiline keyswitch and, more particularly, to the engagement of a line button and a hold button with a release plate by means of pins for locking and releasing the line button.
Key assemblies, such as those used in multiline telephones, employ line buttons connected to separate circuits for making electrical contact with the respective circuits. In addition, the key assemblies include hold buttons which lock and release the line buttons by means of a locking device incorporating a release mechanism. In one common form of locking device, a sliding plate is provided with a tongue and groove configuration for engagement of pins extending transversely from the keys. Movement of the plate provides the lock and release functions. Locking occurs by movement of the plate induced by activation of a line button. Release is accomplished by movement of the plate induced by activation of a hold button. Springs are employed for returning the line button, the hold button, and the plate to their respective rest positions. The plate is frequently referred to as a release plate. The release mechanism concerns the specific configuration of pin and plate whereby the release plate is set into motion by activation of the hold button.
A problem arises in that release mechanisms which have been employed heretofore have required more manual labor and more costly parts in the manufacturing process of keypads than is desirable. This problem may be better understood by consideration of presently available key assemblies.
One form of key assembly employs a torsion spring with a pin attached thereto, the pin sliding in a vertical slot of the release plate. A rib is located on a hold button plunger to operate against the assembly of pin and torsion spring in order to move the release plate. Movement of the release plate releases a depressed line button on the return stroke of the hold button. The hold button is spring loaded, the spring providing for the return stroke upon release of the hold button by a person using the key assembly. The foregoing assembly of the key assembly is labor intensive and subject to adjustment problems during assembly.
As a further example of a presently available key assembly, the key assembly employs a flat cantilever spring having a tab on the end of the spring which serves as a pin integrally formed with the spring. The release plate includes an inclined surface against which is pressed the tab of the spring during operation of the release mechanism. Movement of the release plate releases a depressed line button on the return stroke of the hold button. While the design of this key assembly is simpler than that of the previous example, this key assembly suffers the disadvantage of high cost associated with the fabrication of the flat cantilever spring, which spring has a complex shape. Also, the tab on the end of the spring causes excessive wear on the release plate. As a result, a more expensive plastic material must be used in the manufacture of the release plate than would otherwise be required in order to minimize such wear.